A comprehensive study on the impact of Gd substitution on structural, optical and magnetic properties of ZnO nanocrystals

Abstract We report here the impact of Gd substitution on structural, optical, photoluminescence and magnetic properties of Zn1-xGdxO (x=0.02-0.10) nanocrystals. Rietveld refinement of PXRD patterns, SAED and FTIR analysis revealed that Zn1-xGdxO nanoparticles crystallize in single phase wurtzite type hexagonal symmetry. HRTEM & SEM analysis confirmed good crystallinity of Zn1-xGdxO nanocrystals with a wide size distribution in 10-40 nm range. Concentration of Gd3+ ions at the Zn site causes a systematic reduction in the average crystallite size of Zn1-xGdxO nanocrystals. UV-Vis-NIR and photoluminescence spectroscopic studies showed decrement in band gap energy and suppression of UV emission (391-416 nm) with Gd concentration in Zn1-xGdxO. Analysis of the visible band emission spectra demonstrated that 325 nm photoexcited Zn1-xGdxO nanocrystals emit light in the orange-red region due to formation of complex defects in the ZnO lattice. M-H curves of 2% and 4% Gd doped ZnO nanocrystals recorded at 300 K showed thin ferromagnetic hysteresis loop (almost equal Mr=~1.8memu/g and Hc=~210 & ~136 Oe for 2% and 4% Gd doped ZnO respectively) at lower magnetic fields but in the high field range, the magnetization responded linearly with the applied magnetic fields and, thus establishes coexistence of paramagnetic and weak ferromagnetic ordering in 2% and 4% Gd substituted ZnO nanocrystals. The higher 6%, 8% and 10% Gd substituted ZnO nanocrystals are found to be paramagnetic at 300 K. At 5 K, all the samples showed S-shaped M-H curves with negligible coercivity & retentivity and the magnetization monotonically incremented (5-25 emu/g) with increasing Gd concentration in ZnO. Superparamagnetic clusters and antiferromagnetic states coexist in Zn1-xGdxO nanocrystals at 5 K. Magnetic and optical properties of Zn1-xGdxO nanocrystals are suitable for magneto-optoelectronic applications.